Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (DASD) such as a disk drive incorporating a rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces, and magnetic heads are used to write the data to and read the data from the tracks on the disk surfaces.
Data is written onto a disk by a write head that includes a magnetic yoke having a coil, passing there through. When current flows through the coil, a magnetic flux is induced in the yoke, which causes a magnetic field to fringe out at a write gap in a pole tip region. It is this magnetic field that writes data, in the form of magnetic transitions, onto the disk. Currently, such heads are thin film magnetic heads, constructed using material deposition techniques such as sputtering and electroplating, along with photolithographic techniques that include the use of photoresist masks.
Examples of such thin film heads include a first magnetic pole, formed of a material such as NiFe which might be plated onto a substrate after sputter depositing an electrically conductive seed layer. Opposite the pole tip region, at a back end of the magnetic pole, a magnetic back gap can be formed. A back gap is the term generally used to describe a magnetic structure that magnetically connects first and second poles to form a completed magnetic yoke as will be described.
One or more electrically conductive coils can be formed over the first pole, between the pedestal and the back gap and can be electrically isolated from the pole and yoke by an insulation layer, which could be alumina (Al2O3) or hard baked photoresist.
A P2 pedestal is often formed above the first pole in the pole tip region, and is separated from the first pole by a non-magnetic write gap layer. This P2 pedestal extends to the ABS of the head and defines the track width of the head. This pedestal is also used to define the width of a self aligned notch, or pedestal, on the first pole. This is achieved by using the P2 pedestal as a mask and then ion milling through the write gap layer and into a portion of the first pole. An angled ion milling operation can then be performed to removed redeposited material from the sides of the notch or pedestal formed on the first pole. A second pole formed over the P2 pedestal completes the magnetic yoke, being magnetically connected with the first pole by the write gap and stitched to the P2 pedestal.
As those skilled in the art will appreciate, the P2 pole or pedestal is a critical element of the write head. This is because it defines the track width. Also it must be constructed of a material that has high saturation, and low coercivity. It must have a high aspect ratio so that it will be narrow enough to provide the necessary small track width while being tall enough (in the track width direction) to provide sufficient overwrite performance. This P2 pedestal becomes the focal point for the magnetic flux in the write head.
Traditionally, such P2 pedestals have been constructed by forming a photoresist frame having a trench in which the P2 pedestal is plated. The photoresist frame use to form the P2 pedestal has currently been constructed using Deep U.V. photolithography. Deep U.V. lithography provides better resolution and would provide better track width control, but have some limitation to pattern very thick photoresist frame.
With reference to FIG. 1A, using Deep U.V. photolithography, a photoresist frame 101 is constructed that has a trench 102 in which the P2 pedestal 104 can be plated. Due to the nature of the photolithographic process used, the trench has a relatively constant width (low sigma) at its lower and center portions, but widens significantly at its upper portion, forming a flare 106. Magnetic material 108 is plated into the trench 104, and forms a bulb 110 at its top due to the flare 106 of the trench and due to the height to which the magnetic material 110 must be plated. It should be pointed out, that due to the chemical mechanical polishing process used, the magnetic material, must be plated much higher than would otherwise be necessary, for example 0.8 microns higher than the height of the finished P2. After, the magnetic material 110 has been deposited, the photoresist frame 102 can be lifted off.
With reference now to FIG. 1B, an alumina fill 112 is deposited to completely cover the magnetic material 108. A chemical mechanical polishing (CMP) process 114 is performed to remove the alumina opening up the top of the P2 pedestal, and bringing the magnetic material 110 down to the desired level 116 of the finished P2 pedestal. Those skilled in the art will appreciate that processes such as electroplating and chemical mechanical polishing non-uniformity across a wafer. Therefore, in order to assure that all P2 pedestals on a wafer are opened up by the CMP process, about 0.8 microns of additional P2 height must be plated just so that it may be then removed by the CMP. This additional P2 pole material, which must be removed by CMP significantly decreases throughput time. Plating time alone is increases by 25%, just to plate the additional 0.8 microns of P2 material, and the increased CMP requirement further increasing process time.
More importantly, the P2 height required by the CMP process prevent the use of Deep U.V. photolithography. If the additional P2 height were not necessary, the photoresist frame height would be shallow enough to allow the use of Deep U.V. lithography, which would result in tighter sigma (ie width variation) and a higher aspect ratio of the P2 pole, and a better track width definition.
Therefore, there is a strong felt need for a process for removing alumina material to open up a magnetic structure without necessitating the removal of a significant amount of the magnetic structure itself. Such a process would virtually eliminate the need to overplate the structure, would increase throughput time by decreasing process time, and would allow the use of more precise higher resolution lithographic techniques, resulting better defined, higher aspect ratio magnetic structures on write heads.